1. Field of the Invention
The present invention generally relates to methods for increasing the adhesion of a terminal to the top copper wiring level in semiconductor devices.
2. Description of the Related Art
Conventional systems have improved the adhesion of silicon nitride to an interior copper wiring surface by the addition of an intervening copper silicide layer. For example, as described in U.S. Pat. No. 5,447,887 to Filipiak et al., hereinafter "Filipiak" (incorporated herein by reference), the connections of internal levels within a semiconductor device are improved with an intervening copper silicide layer.
The silicide layer is conventionally formed within a plasma enhanced chemical vapor deposition (PECVD) reaction chamber by introducing silane (SiH.sub.4) in the absence of a plasma into the chamber. The silane reacts with exposed copper surfaces to form copper silicide. After a sufficient thickness of copper silicide is formed, plasma is generated and gases are introduced into the reaction chamber for deposition of silicon nitride onto the device, including onto the copper silicide layer. The intervening copper silicide layer acts as an adhesion layer between the silicon nitride and the copper.
Filipiak teaches that a silicide layer approximately 100 angstroms (100 .ANG.) thick is sufficient to significantly increase the adhesion between the nitride and copper. More specifically, Filipiak explains that, as a general rule, the thickness of a silicide layer should not exceed 10% percent of the total thickness of the copper. A reason for limiting the thickness of the silicide layer to less than 10% of the total copper thickness is that the silicide degrades the resistivity of the copper. While generally the silicide layer should not exceed 10% of the total thickness of the copper interconnect, Filipiak shows that a silicide layer thinner than 100 angstroms (100 .ANG.) or less than 2% of the total copper thickness is sufficient to significantly improve the adhesion of a subsequently deposited PECVD silicon nitride film to the copper member.
However, Filipiak's method is limited specifically it does not provide sufficient coverage or uniformity and, consequently, it does not provide the required adhesion strength for the terminal layer to remain connected to the last metalization (LM) layer. The invention described below solves the above problem.